Tutorial: Changing Levels Last edited 2 months ago2024-03-13 06:30:43 UTC

A quick and dirty guide to perfect level changes

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Level changes are often over explained, and too complicated for their own good. There really is nothing to them and if you follow this tutorial step by step, you should have absolutely no trouble whatsoever.

What is a level change?

A level change is, simply put, a transition or displacement from one map (.bsp file) to another. And the reason you're reading this is because you're lost or trying to get a level change to work properly.

Why do I need level changes?

If you're thinking to yourself: "I can get by without them, and save myself a lot of hassle...", then think again!

Half-Life maps have limits. These limits should never be reached or pushed, you can read more about these in the general MAX_MAP limits part of Tommy14's errors page. If your levels are getting too big you should consider splitting them into 2 or more separate levels to avoid reaching these limits. This can be really useful for reducing r_speeds when working with two or more complex areas, or just to help you keep track of where you are in your map. Huge detailed maps are really difficult to work with in Hammer, as you probably already know.

How do I create level changes?

There are 3 types of level changes:

Seamless level changes

The only entities you'll need - since you just want a simple level change - will be trigger_changelevel (one in each map) and an info_landmark (also one in each map).

Start by making a suitable corridor:
A suitably suitable corridorA suitably suitable corridor
Now to add the info_landmark. Read very carefully is these details are critical:

The info_landmark sets up a constant point of reference in the origin and destination maps. It must appear in both maps otherwise the level change will not work correctly. The origin and destination info_landmark must both have the same Name (targetname)
Always put names of maps and info_landmarks in lowercase!!! And do not use spaces or other characters except numbers and letters, _ underscores are ok.
So basically, it's the same info_landmark in both maps.
The Origin map trigger_changelevel:
Set these properties you need to change:

New map name: map2
Landmark Name: landmark1 (or whatever you called your two identical landmarks - one in each map)
The Destination map trigger_changelevel:
Set these properties you need to change:

New map name: map1
Landmark Name: landmark1 (or whatever you called your two identical landmarks - one in each map)
Make sure the trigger_changelevel brushes are far enough away from each-other (relatively speaking) that the player cannot touch the trigger going back to the previous map as soon as they've entered the second map through the first level change. If they are too close, the engine will block all level change triggers that occur in the map from that point onwards!
To avoid this problem, make sure the level change triggers in the two maps have at least 56 units between them. Players are 32 units wide and long, but their bounding box can become larger if they walk through at an angle. 56 units is enough space to avoid this problem.
Relative DistanceRelative Distance
Now, compile the maps through hammer or any other front-end compiler but remember not to run the game!, fire up hl with the console, and test the transition. If you did this correctly you should seamlessly jump from one map to the next no matter how you enter the trigger_changelevel.

One way level changes

You would think a one way level change would only require one trigger_changelevel?


You have to set the level change up exactly as you would for a normal change. The difference is that in the second map, reduce the size of the trigger_changelevel brush and move it somewhere that the player cannot get to it. That is what stops the player from going back. Also check the Use Only Flag just to make sure those NoClipping players still can't get back.

Teleporting level changes

A teleporting level change is a bit more involved but is actually a lot less of a headache, provided you're only going to make it a one-way affair. It can also be a cheat a modding team can use when passing between chapters where team A work on the previous chapter, and team B work on the next, without worrying about passing the transitional level geometry between the two.

We will assume 2 maps map1 and map2 and the setup is a one-way teleport from map1 to map2.
map1 setup
In map1, the setup would involve a tiny player-sized room (slightly above 32x32x72), textured with BLACK (or WHITE, whichever you fancy), with these three entities overlapping each other:
  • info_teleport_destination placed on the floor
    • Name: tp_to_map2
    • Pitch Yaw Roll or Angle: (facing where you want the player to face in the destination map map2)
  • trigger_changelevel placed covering the whole room
    • New map name: map2
    • Landmark: tp_landmark
  • info_landmark placed at least 36u above the floor
    • Name: tp_landmark
And then elsewhere in map1, have a trigger_teleport target tp_to_map2 in our setup (with delay if desired).
User posted image
map2 setup
In map2 the setup can go two ways; the easy way (with favourable conditions) or the other way.

If in the previous map's teleport room the player's position is well constrained close to the info_landmark and the info_teleport_destination is already facing the correct way, then it's simply a matter of placing a single info_landmark at the destination point:
Otherwise, another teleportation room is warranted to "catch" the player and place them in the correct position. This room should be bigger than the room in the previous map (about 2x, but can go higher just to be safe). Place the following entities: And finally, in the main level:
  • info_teleport_destination placed on the floor
    • Name: tp_dest
    • Pitch Yaw Roll or Angle: (facing where you want the player to face)
And don't forget the obligatory [non-functional] return trigger_changelevel!:
  • New map name: map1
  • Landmark: tp_landmark
  • Flag: ☑️ USE Only (2)
User posted image

Common problems and solutions

Players stuck in a random place at the other end
Don't forget to add the return trigger_changelevel! Even for testing, the setup pair needs to exist on both maps.
This is exactly what happens when you changelevel through the inaccessible broken elevator in "Forget About Freeman!"
Players transition seamlessly but now stuck at the other end
Make sure both info_landmarks are at the same position relative to the level geometry in the transition area. For example, you cannot have landmark1 16u above the floor in map1 but then have landmark1 64u above the floor in map2. This applies to walls as well.

You may be tempted to offset one of the landmarks to fix a problem, but that's actually creating this exact problem going the other way. Just make sure the landmark is identically positioned.
Some error occurred and now all level changes don't work
You had the two trigger_changelevels too close to each other, making it so that as soon as you changed level, you're inside the other trigger_changelevel. The game engine will freak out about this and disable all level transitions.

The solution is to have the trigger_changelevels further apart from the center of the transitional area. It should be about 56u apart or more face-to-face when you compare the two maps.
I can't make a level change that rotates 90° (or some other angle)
Unfortunately, no you can't (at least not in vanilla Half-Life). The orientation of the transitional areas need to be identical.
Objects (like pushable crates) disappear at the transition area
Brush entities need a unique global name to be able to be "carried over" across levels.


Commented 15 years ago2008-07-24 03:43:29 UTC Comment #100615
great tutorial ;)
Commented 15 years ago2008-08-03 13:59:00 UTC Comment #100616
When I loaded the next level, I was outside of the map. Can anyone help me? :(
Commented 15 years ago2008-10-05 20:40:54 UTC Comment #100617
couldnt be explained clearer.
Commented 15 years ago2009-01-24 19:30:37 UTC Comment #100618
it crashes when i get on the 2nd map
Commented 14 years ago2009-06-10 23:56:06 UTC Comment #100619
great tutorial thanks! i set up everything the way you said, but i get "stuck" when i arrive at map2, that is, i can't move, even with noclipping!
Commented 14 years ago2009-09-14 04:19:55 UTC Comment #100620
Why don't I have trigger_changlevel?
Commented 13 years ago2010-10-11 04:25:36 UTC Comment #100621
it crashes for me too, i cant get it to work!
Commented 13 years ago2011-02-19 06:52:39 UTC Comment #100622
If its crashing, make sure your landmarks have the SAME name, and that BOTH levels, regardless of one way or both ways, have the trigger AND a landmark. I just had that problem, and now my map works.
Commented 12 years ago2011-08-24 00:06:36 UTC Comment #100623
Also make sure you've actually compiled both maps before running the game. Yeah, that has happened to me. Twice.
Commented 9 years ago2015-03-26 22:07:25 UTC Comment #100624
Moreover this trigger_changelevel method allows the following entity persistence !
Commented 8 years ago2015-07-23 02:16:49 UTC Comment #100625
Why is it taking me back to the loading screen where I choose the player and teams?
Commented 8 years ago2015-08-17 08:15:46 UTC Comment #100626
Good tutorial it's just that I'm stuck when on the second map...
Commented 8 years ago2015-11-10 01:53:51 UTC Comment #100627
I had a problem with a levelchange, maybe it helps someone what I found out.

I have three maps and the player traverses them in this order:

Map a
Map b
Map c

The transition between Map b and Map c didn't work because the trigger_changelevel from "map a" to "map b" had a wrong "New map name", like "Map C". So I guess The Value you type in for "New map name" is Case-Sensitive.
Commented 8 years ago2016-05-24 08:40:17 UTC Comment #100628
I made two test maps for an HL mod I want create.

The transition from 1st map to 2nd map worked correctly.

But when I tried to return to 1st map, it didn't worked. Why?
Commented 7 years ago2016-05-29 11:59:17 UTC Comment #100629
alright, the level change work for me, only one issue: since my level change is in an elevator, i have npcs from the previous level who shows up in the next level, but i really dont need them in here, so how do i get rid of them?
Commented 7 years ago2016-10-01 06:17:55 UTC Comment #100630
Me works, but the npcs of the another map continue in the new map? Why?
Commented 3 years ago2021-03-09 00:47:21 UTC Comment #103401
Never intersect the trigger changelevel, bcoz the trigger to get to the other map doesnt work, and thats was my error, the game change the map when I get into the intersection and the trigger doesnt work anyway. :confused:
On the superior of the screen it say : CHANGELEVEL Map1 Map1toMap2
The error was solved when I moved the trigger a bit more far than the other. Thanks for read.
Commented 2 years ago2021-08-11 15:56:42 UTC Comment #103664
why can't you do one-way level change by omission? does it affect some parts of the game?
Commented 2 years ago2022-01-31 15:46:04 UTC Comment #104066
I often keep Half-Life running in the background while I make small changes and quickly recompile maps. I then restart the map through the console and test again. I can verify that this is a bad way to test trigger_changelevels. Even though it's all perfectly set up, I ended up on world coordinate 0,0,0. You really have to restart Half-Life completely if you make any changes to the changelevel triggers.
Commented 6 months ago2023-11-27 19:24:33 UTC Comment #105663
when i play my first map and walk into the trigger, it spawns me out of bounds, i did everything. HELP PLS.
EDIT: fixed it. i put a info_player_start in the second map and it was interfering.

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